A multinational project led by British researchers aims to use a high-power laser to reproduce the physical reaction that occurs at the heart of the sun and every other star in the universe - nuclear fusion. If the project succeeds it has the potential to solve the world energy crisis without destroying the environment.

The scientists admit that a commercial reactor is a long way off, but they believe the laser approach to producing fusion shows great promise. The EU is considering a proposal to fund the set-up costs for a seven-year research project called HiPER - high powered laser energy research - that would build a working demonstration reactor. Preparing for the seven-year project alone, which is a collaboration of 11 nations, is expected to cost over €50m (£34m). Actually building the reactor itself will cost over half a billion euros.

The British-led project, which has been earmarked by the EU as a priority, is designed to leapfrog an American-funded project called the National Ignition Facility (Nif) in Livermore, California. When that is built in 2010, physicists are confident that the Nif laser will be powerful enough to start a fusion reaction. Experiments in the Nevada desert in the 1980s with underground explosions of nuclear weapons have already shown how much energy they will need to deliver with the laser.

Mike Dunne, director of the Central Laser Facility at a publicly funded research site in Oxfordshire that houses Vulcan, the most powerful laser in the world, said: "The world is going to take notice when this happens. Politicians are going to look around and say, 'So what are you going to do about it? What's the next step?'. This is how to take it from a scientific demonstration to a commercial reality."

Prof Dunne said that many of the details of the nuclear tests were still classified, "but the only thing that matters to us as a bunch of energy scientists is that it does work. The trick now is, can we get it to work without throwing a nuclear bomb at the thing?" That is what Nif is designed to do.

Achieving fusion on Earth in a way that will release useable energy has long been an aspiration of physicists.

The idea is to fuse two atoms of hydrogen to form helium. The reaction that powers the sun releases large amounts of energy because it turns Einstein's famous E=mc² equation on its head. A small amount of mass is lost when the hydrogen atoms combine, in the process releasing vast quantities of energy.

Unlike nuclear fission, only low-level radioactive material, no more dangerous than hospital waste, is left over afterwards. And best of all, a runaway chain reaction like the one that caused the Chernobyl meltdown is simply impossible. The fusion dream is already being pursued by a €10bn project called Iter - international thermonuclear experimental reactor - which is being built in Cadarache, France. This project aims to use powerful magnets to fuse the hydrogen atoms. But many in the laser research community see their approach of bombarding hydrogen with a high energy laser as the more promising route.

"The beauty of the laser approach is that you can divide and conquer," said Prof Dunne. There are formidable engineering challenges in building a high enough power laser, increasing its firing rate and designing the millimetre sized fuel pellets, but these can all be pursued in parallel, he said.

Others are more sceptical about the laser approach. Duarte Borba, who works at Jet, an experimental magnetic fusion reactor, said achieving ignition was not the be-all and end-all. "There is a long process still ahead before you can actually build a reactor based on laser fusion," he said.

Benefits and snags

Nuclear fusion Process in which two isotopes of hydrogen - deuterium and tritium - are combined to produce helium, a neutron and huge amounts of energy.

Deuterium or heavy hydrogen Conventional hydrogen is made up of a proton nucleus with an electron spinning around it. The nucleus of a heavy hydrogen atom contains a proton and a neutron.

Tritium or super-heavy hydrogen Its nucleus contain a proton and two neutrons. It is moderately radioactive and can be manufactured from the metal lithium.

Environmental benefits Nuclear fusion does create some low-level radioactive waste, but nothing more dangerous than you would find in a hospital. The reaction does not produce carbon dioxide so it will not contribute to the greenhouse effect and a Chernobyl-style meltdown is impossible.

Problems The biggest challenge will be to build a powerful enough laser that can fire rapidly enough. The world's most powerful lasers need several minutes to reset for a second shot. A laser fusion reactor will need to fire several times a second. Scientists will also need to develop materials durable enough for the laser bombardment.